This invention relates to a station selecting device employing an improved signal discriminating method and apparatus for use in a communication transmitter-receiver, a broadcasting receiver, and the like where the receiver, for example, is provided with an automatic station selecting device.
Recently, the number of communication stations utilizing transmitting-and-receiving apparatus and the like has increased significantly, particularly in the 2 m band. Thus, it has sometimes been difficult to find vacant channels in the ordinary communication or to find an opposite station in a substantially less-crowded band or in a special time period such as around midnight. Furthermore, difficulties have been experienced with radio broadcasting receivers and particularly automobile radio receivers, where it is comparatively difficult to select stations, the number of which has been thus increased.
To avoid these inconveniences, some transmitter-receivers have recently been equipped with an automatic station selecting device having so-called autoscanning and autotuning functions which sweep, normally during signal reception, the channels or stations to automatically select and transfer the channels. In the automatic station selecting device, the automatic sweeping and stopping are controlled by detecting or discriminating the existence or nonexistence of a sensing signal in the desired channel and tuning is effected thereafter. However, in conventional methods and circuits, the discrimination has been effected by applying, for example, a switching pulse and a squelch signal output to a NAND gate. This, in turn, has resulted in the possibility of erroneous operation by a random noise signal.